The present invention relates to a method for machine aided combination of NIR material concentration measurements with the spectroscopic evaluation of glass fibers, fitted with fiber Bragg gratings (FBGs) for measuring temperature profiles.
It is customary to use Fourier transform near-infrared (FT-NIR) spectrometers for online measurement of material concentrations in complex material mixtures in chemical pharmaceutical plants (see PROCESS, April 2003 “Bessere Daten für effizientere Prozesse” [“Better data for more efficient processes”]. These units are currently to be found in processing designs having optical multiplexers for the operation of a number of optical probes (for example from Bruker, Matrix-F). The essential optical components are integrated in these spectrometers (light source, interferometer, detector, reference laser for the wavelength calibration of the interferometer). In order to obtain a good signal-noise ratio, use is made for process coupling of multimode glass fibers (MM glass fibers) with a large light-carrying cross section (several 100 μm). The spectrometers themselves are of high resolution and cover a large spectral bandwidth (approximately 800 nm to 2.5 μm).
As regards temperature profile measurement by means of FBG fitted glass fibers [see DE 0403132404 A and, for FBG technology see R. Kashyap, “Fiber Bragg Gratings”, Academic Press, 458 (1999), www.inventivefiber.com.sg/FBG.html, K. O. Hill et al:, Appl, Phys. Lett. 32, page 647 (1978)], which is already based in principle on the use of comparatively optically weak single mode glass fibers (SM glass fibers), the optical components have decidedly different properties than in the case of the material concentration measurement via FT-NIR spectroscopy. Since the application of FBG technology resides originally and to a greatly predominant extent in optical telecommunication, the corresponding optical components are also specifically tuned to the requirements of this technology. Usually narrowband, high-resolution diode array spectrometers or scanning laser light sources or fiber spectrometers are used. The light sources are adapted to the spectrometers (SLEDs (Superluminescent Light-Emitting Diode) or scanning laser sources), and have typical bandwidths of a few tens of nanometers.
The two technologies (FT-NIR for determining material concentration and spectroscopy on FBG fitted glass fibers) have an overlap in the spectral region used and in the possible application in chemical-pharmaceutical apparatuses, in apparatuses of petrochemistry, in particular refineries, and in apparatuses of the food processing industry (Reactors, columns (for example for distillation, extraction or for drying), crystallizers, dryers, furnaces, specifically microwave-heated or induction furnaces). This points to the need for a common equipment basis.
Starting from the prior art, the object therefore was that of modifying the optical components and/or their assembly such that the two measuring probes (process light barriers for concentration measurements and FBG fitted glass fibers for temperature measurements) can be operated using the same equipment basis, preferably optical multiplexing.